Control system



Oct. 10, 1939. R. R. HOWE 2,175,729

CONTROL SYSTEM Filed Oct. 1, 1934 Patented Oct. 10, 1939 UNITED STATES PATENT OFFICE- CONTROL SYSTEM poration of Delaware Application October 1,

Claims.

This invention relates to control systems and particularly to systems for controlling the dynamo electric machines used for tensioning materials being wound upon and unwound from 5 reels or similar winding and unwinding mechanisms.

In systems of the above type, it is often desirable to maintain a predetermined tension on the reeled material. Dynamo electric machines have been mechanically coupled to the reels and utilized to tension the material being reeled by energizing the machines so that one tends to wind the material on the winding reel and the other machine runs as a generator tending to prevent unwinding of the unwinding reel. As the material is wound and unwound the effective diameters of the reels change and hence the tensioning pull transmitted by the machines must change accordingly in order to maintain the tension on the material.

Various mechanisms mechanically actuated by the tension or slack in the reeled material have been utilized to control the excitation of tensioning machines of the above type but these of necessity are either delicate mechanisms that easily get out of working order or if sufiiciently rugged are not sufficiently accurate and stable to maintain the tension at the desired value. Such mechanical devices such as rollers actuated by the slack in the strip are physically in the way and are also undesirable due to the fact that they leave a mark on the strip of material.

It is an object of this invention to provide an improved system for controlling the dynamo electric machines in tensioning systems of the above type that avoids the above disadvantages and solves the above problem in an efiicient and novel manner.

It is a further object of this invention to provide-a tensioning system that is simple, rugged and yet is sufficiently sensitive to maintain a constant tension.

These and other objects and advantages are obtained by this invention, the various novel features of which will be apparent from the drawing and description herein and will be more particularly pointed out in the claims.

As illustrated example of an application of this invention is shown in the accompanying drawing, in which:

Figure 1 is a diagrammatic showing of a tensioning system embodying a form of the invention;

Big. 2 is an illustration showing one manner 1934, Serial No. 746,361

of utilizing the tensioning system shown in 1 in a strip rolling mill.

Referring to Fig. 2 of the drawing, a strip rolling mill is shown wherein the main drive motor I2 may be mechanically connected to a reel I5 or IE to pull a strip of material (4 through rolls I! which perform an operation on the strip. The clutch mechanisms, generally designated as H] and 2!), determine which reel is connected to the main drive motor. Connected to each of the reels l5 and 86 are dynamo electric machines 8 and 9 the field wind ings of which are oppositely energized so that the forward or winding machine runs as a motor tending to aid the main drive motor. The trailing machine, that is, the machine connected to the unwinding reel, is connected to run as a generator thereby acting as a brake to tension the strip of material between the unwinding reel and the rolls l1. It is the usual practice to reverse the drive, running the strip back and forth through the rolls in order to have several operations performed. Hence upon reversal of the drive, the trailing reel ofvthe last pass becomes the winding reel of the next pass. It is desirable therefore that the tensioning machines 8 and 9 be so connected and so energized and controlled so that the strip may be easily reversed and so that the trailing machine will always supply a predetermined tension to the strip.

If the reel diameters were constant, a constant tension could be applied to the trailing reel by energizing the trailing reel machine so that it would apply a constant torque to the trailing reel. However, as the trailing reel unwinds the effective reel diameter decreases and hence the lever arm through which the braking torque is transmitted from the reel to the strip is shortened and the braking torque of the trailing machine must decrease accordingly, in order to maintain the tension at the desired value.

In Fig. 1 there is shown a control system in which the strip direction may be easily reversed and in which the trailing tensioning machine will maintain a. constant back pull on the strip. The main drive motor I! is energized by a generator 6 which is driven by synchronous motor 5 which also drives an auxiliary generator I. The synchronous motor 5 is energized from the alternating current source 40. The tensioning machines 8 and 9 have their armatures connected in series across the terminals of the auxiliary generator I. The field windings 28 and 29 or" the back tension machines are oppositely connected in parallel to the direct current source i l, so that one machine will run as a motor while the other runs as a generator. The parallel field windings are connected in series with the resistance 33 of a differential regulator generally designated as which has a contact 3Q actuated by solenoids 35 and 35. The coils 35 and 36 are responsive to the voltages across the machines 8 and 9 respectively and movement of the contact 34 acts to increase the field current of one machine and simultaneously decrease the field current of the other machine.

To consider the operation of the system the strip is considered to be moving in the arrow direction, the clutch 2U coupling the main drive motor l2 to the reel l6 which will be the winding reel. As the mill is brought up to any desired speed by manipulation of the rheostat 31, a constant horsepower input to the motor I2 is maintained by the regulator generally designated as l3. As the current in the armature circuit of the main motor tends to increase with the building up of the strip on the reel IS the regulator l3 is operated to increase the current in the field winding 22 thus tending to decrease the motor armature current and maintain it constant. With constant horsepower input and the increasing torque requirement due to the building up of the material on the reel IS, the speed of the main motor 12 decreases directly as the diameter of the reel is increases. The speed of the reel l6 and motor 9 likewise decreases as they are mechanically connected to the motor lit. However, the lineal strip speed remains constant as the decrease in the speedoi the reel it is compensated by the building up of the strip on the reel.

As the speed of the machine 9 decreases its counter-E. M. F. decreases. However, as the size of this machine is generally one-tenth that of the main driving motor, this change has little efiect upon the mill drive. The trailing machine 8 is pulled by the strip of material and because of the energization of its field 28 it runs as a generator supplying a torque to the reel and there by supplying the desired tension to the strip of material. As the strip of material unwinds from the reel iii, the machine 8 increases its speed in direct proportion to the diameter of the reel As the speed of machine 8 increases, the generated E. M. F. across its terminals increases. These changes in the machine voltages, that is, the olecrease in voltage across the machine and the increase in voltage across the machine coils 35 and 36 to move the contact right as viewed in the drawing. This vs-.. crease the energization of field Winding and increase the energization of the field winding until the machine voltages are again equal. Thus, the flux of each machine is varied in direct proportion to the -rcel diameter change and the torque supplied by the trailing machine decreases as the speed increases, that is, in proportion to the reel diameter change. The desired value of tension is thus maintained throughout the pass.

As the effective voltage across the winding machine is the generated voltage minus the lR drop and the effective voltage across the trailing machine is the generated voltage plus the IR drop, this difference must be compensated in any suitable rnanner. Upon reversal of the generator field M5 by the switch the mill runs in the opposite direction, the main motor l2 eing con.-

enemasnected to reel l5 by the clutch l9, the clutch 20 now being in the position shown. The machine 9 then runs as a generator and in the same mannor as above shown supplies a constant tension to the strip l4.

Although only one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination, a pair of reels adapted to be joined by a length of material, dynamo electric machines connected to each of said reels, a source of current supply connecting the armaturcs of said dynamo machines in series and means con nected so as to be responsive to the voltages across said dynamo machines for simultaneously regulating the excitation of said dynamo machines.

2. In combination, a pair of reels adapted to be joined by a length of material, dynamo electric machines connected to each of said reels, a source of electric energy, means for connecting the armatures of said dynamo electric machines in series with said source, means for oppositely connecting the field windings of said dynamo electric machines in parallel and means responsive to the voltage across each of said dynamo electric machines for regulating the current in one of said field windings inversely with respect to the current in the other or" said field windings.

3. In combination, a pair of reels adapted to be joined by a length of material, dynamo electric machines connected to each of said reels, a source of electric energy, means for connecting the armatures of said dynamo electric machines in series with said source, regulating means responsive to the voltages across said machines for controlling the field windings of said dynamo electric machines whereby a substantially constant tension is maintained on said lentgh of material.

4. A tension regulator comprising a pair of reels adapted to be joined by a length of material, dynamo electric machines connected to each of said reels, a source of electric energy, means for connecting the armatures or" said dynamo elec-- tric machines in series with said source, means i 1 connecting the field windings of said dynamo electric machines oppositely in parallel and means for regulating the current in said field windings whereby a substantially constant tension is maintained on said material, said regulating means comprising a difierential rheostat responsive to the voltages across said dynamo electric machines.

5. In combination, a pair of spaced reels adapted to he joined by a strip of material, dynamo electric machines connected to each of said reels, a source of electric energy, means connecting the armatures 01 said dynamo electric machines in series with said source, means connecting the field windings of said dynamo electric machines oppositely in parallel, a field winding regulator connected so as to be responsive to the difference in voltages across said machines, and means con necting said regulator to said field windings so that both said windings are regulated simul-- tancously.

CHARLES S. Administrator of the Estate 0] Ramos Howe, iiecccscd. 

